DESCRIPTION

The stack KPI allows querying of kernel stack trace information and the
automated generation of kernel stack trace strings for the purposes of
debugging and tracing. To use the KPI, at least one of optionsDDB and
optionsSTACK must be compiled into the kernel.
Each stack trace is described by a structstack. Before a trace may be
created or otherwise manipulated, storage for the trace must be allocated
with stack_create(), which may sleep. Memory associated with a trace is
freed by calling stack_destroy().
A trace of the current kernel thread’s call stack may be captured using
stack_save().
stack_print() may be used to print a stack trace using the kernel
printf(9), and may sleep as a result of acquiring sx(9) locks in the
kernel linker while looking up symbol names. In locking-sensitive
environments, the unsynchronized stack_print_ddb() variant may be
invoked. This function bypasses kernel linker locking, making it usable
in ddb(4), but not in a live system where linker data structures may
change.
stack_sbuf_print() may be used to construct a human-readable string,
including conversion (where possible) from a simple kernel instruction
pointer to a named symbol and offset. The argument sb must be an
initialized struct sbuf as described in sbuf(9). This function may sleep
if an auto-extending struct sbuf is used, or due to kernel linker
locking. In locking-sensitive environments, such as ddb(4), the
unsynchronized stack_sbuf_print_ddb() variant may be invoked to avoid
kernel linker locking; it should be used with a fixed-length sbuf.
The utility functions stack_zero, stack_copy, and stack_put may be used
to manipulate stack data structures directly.